The broad aim of the project is to develop improved clinical applications of cardiac electrophysiology. The methods employed are animal experimentation, observations on patients and computer and graphic modeling. One of the specific objectives is the development of an improved electrocardiographic examination for clinical use. In relation to this objective, a 32 lead system which predicts the total body surface potential distribution has been developed and its diagnostic utility is being evaluated in continuing study of patients. A variety of quantitative descriptors of potential patterns have been derived including separation of dipolar and non dipolar components, displays of deflection areas and others and their diagnostic utility is being evaluated. Both clinical and experimental evidence that states at high risk of ventricular arrhythmias can be recognized by analysis of QRST deflection areas has been obtained and further studies are in progress. Studies of the maturation and cardiac distribution of autonomic effects on cardiac electrophysiology are continuing. Detailed studies of the activation sequence in ischemic myocardium are being carried out with multiple simultaneous bipolar electrograms. A computer model of cardiac fibrillation is being used to investigate the influence of localized lesion size and geometry on vulnerability.